ONE OR MORE gunmen opened fire at a crowded Montreal church dance early Sunday, slightly wounding seven partygoers, Montreal police said. Police said shooting broke out just after 1 a.m. in the Pascal Baylon church basement, which was packed with about 300 members of a Montreal black immigrant community . . . A MASKED BANDIT shot a Great Neck, N.Y., barroom patron Sunday when his demands for cash were ignored by patrons who thought he was staging a Halloween prank, authorities said. The tavern where the heist occurred had been hit the previous night by a bandit in a ski mask who tried unsuccessfully to fire his gun and fled. Patrons thought the Saturday night incident was a Halloween prank and did not report it to police.